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POEvaluating MongoDB-like JSON Queries in PHP
 

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    <p>Consider the following (rather complicated) query expressed in this JSON object:</p> <pre><code>{ "name": "Kindle Fire", "sale": true, "price": { "$gt": 199, "$lt": 264 }, "price.vat": { // bogus, just to show $a['price.vat'] == $a['price']['vat'] "$lte": 1.2 }, "$or": { "qty": { "$gt": 30 }, "eta": { "$or": { "$lt": 3, "$gt": 30 } } }, "countriesAvailable": { "$in": [ "US", "CA" ] } } </code></pre> <h2>Objective</h2> <hr> <p>I want to parse that JSON so that it evaluates to the PHP equivalent of (where <code>$a</code> is my target data):</p> <pre><code>$a['name'] == 'Kindle Fire' &amp;&amp; $a['sale'] == true &amp;&amp; ( $a['price'] &gt; 199 &amp;&amp; $a['price'] &lt; 264 ) &amp;&amp; $a['price']['vat'] &lt;= 1.2 &amp;&amp; ( $a['qty'] &gt; 30 || ( $a['eta'] &lt; 3 || $a['eta'] &gt; 30 ) ) &amp;&amp; in_array($a['countriesAvailable'], array('US', 'CA')) </code></pre> <p>I have little experience building expression evaluators. My idea is to traverse the query from the innermost level to the outermost level, calling the corresponding <a href="http://docs.mongodb.org/manual/reference/operators/">MongoDB operator</a> methods as needed.</p> <p>Assuming <code>$a</code> matches the query, this would be the evaluation plan:</p> <pre><code>$query = array(); $query['name'] = true; $query['sale'] = true; $query['price'] = array(); $query['price']['$gt'] = true; $query['price']['$lt'] = true; $query['price']['vat'] = array(); $query['price']['vat']['$lte'] = true; $query['$or'] = array(); $query['$or']['qty'] = array(); $query['$or']['qty']['$gt'] = false; $query['$or']['eta'] = array(); $query['$or']['eta']['$or'] = array(); $query['$or']['eta']['$or']['$lt'] = true; $query['$or']['eta']['$or']['$gt'] = false; $query['countriesAvailable'] = array(); $query['countriesAvailable']['$in'] = true; </code></pre> <p>The second step:</p> <pre><code>$query = array(); $query['name'] = true; $query['sale'] = true; $query['price'] = array(); $query['price']['$gt'] = true; $query['price']['$lt'] = true; $query['price']['vat'] = true; $query['$or'] = array(); $query['$or']['qty'] false; $query['$or']['eta'] = array(); $query['$or']['eta']['$or'] true; $query['countriesAvailable'] = true; </code></pre> <p>The third step:</p> <pre><code>$query = array(); $query['name'] = true; $query['sale'] = true; $query['price'] = true; $query['$or'] = array(); $query['$or']['qty'] false; $query['$or']['eta'] true; $query['countriesAvailable'] = true; </code></pre> <p>The fourth step:</p> <pre><code>$query = array(); $query['name'] = true; $query['sale'] = true; $query['price'] = true; $query['$or'] = true; $query['countriesAvailable'] = true; </code></pre> <p>Since all the values are booleans the evaluation ends returning <code>!in_array(false, $query, true)</code>.</p> <p>If a better approach exists, let me know.</p> <h2>Problem: Accessing Parent Array Keys</h2> <hr> <p>I'm stuck trying to get the innermost the elements and the relevant (ignoring operators) array index <em>path</em>, for instance, if I use a <code>RecursiveIteratorIterator</code> I get the correct values for the first iteration:</p> <pre><code>$nodes = new ArrayIterator($query); $iterator = new RecursiveArrayIterator($nodes); $iteratorIterator = new RecursiveIteratorIterator($iterator, RecursiveIteratorIterator::LEAVES_ONLY); print_r(iterator_to_array($iteratorIterator)); Array ( [name] =&gt; Kindle Fire HD [sale] =&gt; 1 [$gt] =&gt; 30 [$lt] =&gt; 3 [$lte] =&gt; 1.2 [0] =&gt; US [1] =&gt; CA ) </code></pre> <p>However, it's of little use since I cannot be sure what <code>$a</code> index the keys are referring to, not to mention that the key values are being overwritten by latter entries and the fact that I can't change their values.</p> <p>I've also tried playing with <a href="http://php.net/manual/en/class.recursivearrayiterator.php"><code>RecursiveArrayIterator</code></a>, but without the <code>hasParent()</code> / <code>getParent()</code> methods it doesn't seem to give me much advantage over simply foreach'ing the array.</p> <p>Any suggestions?</p>
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    1. CO`$a['price'] > 199` will not make no sense when it is an array (`$a['price']['vat'] <= 1.2`).
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    2. CO@dev-null-dweller: Indeed. It's a dummy example, please ignore that.
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    3. COFunction to access Parent Array Keys: http://stackoverflow.com/questions/2504685/php-find-parent-key-of-array#answer-2504778
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